This is a cool map...
Watching the Growth of Walmart Across America (http://projects.flowingdata.com/walmart/)
I wonder different this would look for the world.... how many countries in Walmart in now? How different this would be for restaurant chains like McDonald's and Burger King and KFC?

The site has a ton of other cool maps and visualization examples.

FlowingData | Data Visualization and Statistics (http://flowingdata.com/)

Eric